The Grand Canyon, long believed by many to be 70 million years old, is much younger that that -- 5 to 6 million years old -- a U.S. geologist says.

The Grand Canyon in its current entire form came about when two ancient paleocanyons -- one formed between 50 and 70 million years ago and the other formed 15 to 25 million years ago -- become one giant throughgoing canyon when all of a number of canyon segments, including those only formed in the last 5 to 6 million years, became linked due to erosion from the Colorado River, Karl Karlstrom of the University of New Mexico said.

No one disputes the layers of rock that make up the canyon walls are ancient, dating back as much as 1.8 billion years, but there has been ongoing debate about exactly when the Colorado River began cutting through those layers, forming the giant serpentine chasm that draws millions of tourists.

Karlstrom and colleagues used thermochronology, a dating method that can measure the time when rocks were brought to Earth's surface due to erosion removing the layers of rock above, to date the entire canyon.

"I think we've resolved the 140-year-long debate about the age of the Grand Canyon," Karlstrom said.

While two stretches near the canyon's middle are ancient -- the eastern Grand Canyon is 15?25 million years old, and another stretch downriver is 50?70 million years old -- Marble Canyon, the farthest stretch upriver studied, plus the westernmost Grand Canyon, were carved far more recently, he said.

"Different segments of the canyon have different histories and different ages, but they didn't get linked together to form the Grand Canyon with the Colorado River running through it until 5 to 6 million years ago."

Karstrom's study has been published in the journal Nature Geoscience.